Agreed i wouldn't go too low on CP ratio but like 10.5 or 11 would be way better. I'm running 12.5:1 forged internals and the max boost limit of the turbo before knock is approximately 8-10psi.
Im not sure why but more boost = more power even though the overall cp is the same. My guess is that its less of a fighting force as the piston comes up so less power is waited on the compression stroke. More power in boost less power out of boost.